This proposal hypothesizes that reinfection with CMV occurs frequently in some populations, with symptomatic congenital CMV infection occurring in offspring of immune mothers more frequently than previously recognized. Therefore, a case-control study of intrauterine CMV transmission among young women (less than 20 years of age) who were CMV seropositive prior to pregnancy is proposed with the following specific aims: (1) to determine the rates of reinfection with CMV among young, low-income CMV seropositive women, (2) to determine whether exposure to young children and sexual behavior are associated with reinfection among seropositive women, and (3) to assess whether maternal reinfection increases risk for intrauterine CMV transmission among women with preexisting immunity and (4) to characterize the antiviral antibody responses in those women who did and did not transmit CMV to their infants.